Why is a colloidal sol stable?
The colloidal particles carry a particular charge and the dispersion medium carries equal but opposite charge. The stability of the colloid is due to these charges only. Due to the presence of these similar and equal charges, the particles of the colloid sol repel one another and cannot combine together to form larger particles which keeps them dispersed in the medium and the colloidal remains stable. For example, in a ferric hydroxide sol, the colloidal ferric hydroxide particles are positively charged, while the dispersion medium carries an equal and opposite negative charge.